As is known in the art, there are a variety of circuits for energizing a load that attempt to improve the overall circuit performance. Some circuits utilize feedback from a load to bias components, such as diodes, to the conductive state to enable more efficient charging of storage capacitors, for example. Exemplary power control, dimming, and/or feedback circuits are shown and described in U.S. Pat. Nos. 5,686,799, 5, 691,606, 5,798,617, and 5,955,841, all of which are incorporated herein by reference.
FIG. 1 shows an exemplary prior art resonant circuit having a feedback path FB via a series capacitor Cs to a point PFB between diodes D1, D2 that form a voltage doubler circuit. An input filter IF includes an inductor L1 and a capacitor C1 to limit the energy from the resonant circuit that goes back out on the line via the input terminals, which can correspond to conventional white and black wires WHT, BLK. While the voltage level of the feedback signal applied to the diodes D1, D2 can be increased by resonance between the various LC elements CF, LR1, LR2, the amount of feedback is limited to an acceptable amount of electromagnetic interference generated by a portion of the feedback signal flowing back out through the input inductor L1 and capacitor C1. That is, some known circuits having feedback from the load can generate significant Electromagnetic Conductive interference (EMC) that degrades circuit performance and limits use of the feedback.
One problem arising in known Compact Fluorescent Lamps (CFL) is the high load voltage against ground, especially under dimming conditions. CFLs are prone to developing high voltages when dimmed, which in turn generate a high level of Electromagnetic Interference (EMI) on one hand and a parasitic lamp current leakage to ground on the other hand, thus significantly reducing the life expectancy of the lamp.
It would, therefore, be desirable to overcome the aforesaid and other disadvantages.